Argon, a colorless and odorless gas, makes up 0.93% of our planet’s atmosphere. This makes it the third most abundant element in our atmosphere after nitrogen and oxygen. Martian atmosphere is richer in this element containing 1.6 % argon.
It is a noble gas, found in group 18, period 3 and the p-block of the periodic table. Argon (symbol Ar) has the atomic number 18 and an atomic weight of 0.93%. Natural argon consists of three stable isotopes the most common being argon-40 (99.6003%). The other two isotopes are argon-36 (0.3365%) and argon-38 (0.0632%). Older chemistry textbooks show the element’s symbol as A but this was changed to Ar in 1957.
The two British scientists who discovered the element in 1894, Sir William Ramsay and Lord Rayleigh, did so by the fractionation of liquid air. This method is in use today for the production of oxygen, nitrogen and argon as well as two other noble gases - neon and xenon. It has a very small temperature range at which it is liquid with a melting point of minus 189.35°C (83.80 K, minus 308.83°F) and a boiling point of minus 185.85°C (87.30 K, minus 302.53°F).
The outer electron shell of all noble gases is complete, giving them an oxidation state of zero. This means they are very stable making few if any compounds. This also means that the ionization energies of noble gases are high, that of argon being 15.760 eV.
Until 2000, argon was believed to be completely inert making no known compounds. Its name reflects this inert property as it derives from the Greek word “argos” meaning inactive. In that year, scientists produced the first known compound containing the element. That compound, argon fluorohydride (HArF), has no practical uses as above temperatures of minus 246°C (27.15 K, minus 411°F) it decomposes.
Argon itself has numerous uses. Commonly used to fill light bulbs, as it does not react with the hot filament, it is also used to fill other lighting products such as fluorescent tubes, photo tubes and glow tubes.
Another important use for the gas is as an inert atmospheric shield. Its density of 0.0017837 grams per cubic centimeter is greater than both oxygen and nitrogen so it forms a heavier than air inert blanket over atmospheric sensitive processes. As such, it is of use in the growth of germanium and silicon crystals, the production of titanium and arc welding processes.